The present invention relates to a bonded composite of a first thin-section element of sheet material and a second thin-section element bonded together by bond elements defining a bond pattern. More particularly, one of the contemplated applications for the present invention is in bonding outer cover and body side liner thin-section elements of absorbent articles to one another.
Absorbent articles have been known for a long time as personal care hygiene products. Absorbent articles find use, for example, as diapers, training pants, incontinence products, women""s sanitary pads, and the like. Such absorbent articles are designed and constructed to absorb and store liquid bodily excretions such as urine, menstrual fluid, or blood. Women""s sanitary pads are used, for example, to absorb the liquids excreted prior to, during, and after menstruation.
In absorbent articles, the portions of the article where different layers or components are bonded to each other tend to incur significant stress concentrations and can be susceptible to fracture at such bonded locations. Conventional bond patterns position adjacent bond elements in uniform straight lines and crossing rows. The inventors herein have noted the tendency for the absorbent article to fracture at such bond locations, and for such fracture to proceed along the line defined by the respective side edge of the bond pattern. Conventional bond patterns operate somewhat like the tearing of paper forms along perforated lines of weakness.
The problem addressed by the present invention is two-fold. The first aspect of the problem is to design a bond pattern which is process friendly by having a bond contact area at the bonding nip, which contact area in the nip is consistent over time. Such consistent bond contact area is controlled largely by the bonding lands of a roll participating in a bonding nip where such bonds are created, e.g. by ultrasonic frequency energy using a rotary ultrasonic horn, and corresponding anvil bearing the lands defining the respective bond pattern. Conventional bond patterns, having substantially greater variation in the bond contact area, develop excessive stresses in the bonding apparatus related to developing the bonds, and resulting from those variations, whereby useful life of such e.g. anvil roll is fore-shortened. In addition, the respective ultrasonic horn is unevenly worn due to variability of the bond pattern defined about the circumference of the anvil roll, or nonuniformity of the bond pattern, or a repeated xe2x80x9cbumping,xe2x80x9d shock effect where the bond pattern does not provide for a relatively constant contact area between the bonding surface of the anvil roll and the bonding surface of the ultrasonic horn.
The second aspect of the problem is to provide a bonded composite demonstrating a bond pattern, and an absorbent article implementing the bond pattern, whereby the configuration of the bond pattern attenuates the tendency of the bonded composite or absorbent article to fracture along the bond pattern.
It is an object of this invention to reduce the tendency of bonded composites, or absorbent articles made therewith, to tear at the edge of the bond pattern, by incorporating into the bond pattern bond elements at locations and in configurations which attenuate fracture of the article, and which spread a concentrated stressing force over an increased area of the bonded composite or absorbent article.
It is another object of this invention to provide a relatively consistent bond contact width in the bonding nip, with respect to bonding apparatus, such that variations in the composite contact lengths of the bond elements, across the width of the bond pattern at any location along the length of the bond pattern, are 0.010 inch or less where the composite contact length is, for example, about 0.060 inch.
It is still another object of the invention to provide a relatively consistent bond contact width in the bonding nip, with respect to bonding apparatus, such that variations in the composite contact lengths of the bond elements are no more than 13 percent of the average composite contact length.
It is yet another object of this invention to provide a bond pattern which, when superimposed around the periphery of a horn or anvil roll, attenuates feedback spikes.
This invention comprehends a first family of embodiments defining bonded composites, and absorbent articles comprising such bonded composites. Such bonded composite comprises as a first thin-section element, a first layer of thin-section sheet material. A second thin-section element is bonded to the first thin-section element by bond elements defining a bond pattern. The bond pattern has a pattern length, a pattern width represented by first and second side edges of the bond pattern, and a central longitudinal axis. The side edges of the bond pattern are defined generally by those areas of the respective thin-section elements which participate in absorbing and dissipating, by operation of the bond pattern, stresses received into the bond pattern. The bond pattern reflects application of force urging the first and second thin-section elements toward each other in face-to-face relationship to form an array of separate, distinct, and spaced elongate bond elements in a repeating arrangement affixing the first and second thin-section elements to each other. As ones of the bond elements, a first sub-array of longitudinally-oriented separate and distinct stress receptor elements is disposed proximate the side edges of the bond pattern, and spaced at first common distances from each other along the length of the bond pattern. As second ones of the bond elements, a second sub-array of longitudinally-oriented separate and distinct transfer and dissipation elements is disposed inwardly of the side edges and inwardly of the stress receptor elements, and at second distances from the stress receptor elements less than the spacing of respective ones of the stress receptor elements from each other.
In some embodiments, respective transfer and dissipation elements have first ends disposed on the interior portion of the bond pattern, and extend to second ends adjacent the side edges of the bond pattern between respective ones of the stress receptor elements. The stress transfer and dissipation elements thus direct stresses inwardly to the interior portion of the bond pattern, and dissipate such stresses at the interior portion of the bond pattern.
Bonds corresponding to the bond elements can be activated by application of e.g. thermal energy or ultrasonic-frequency energy to at least one of the first and second thin-section elements.
In preferred embodiments, at least one of the first and second thin-section elements comprises polymeric material selected from the group consisting of polyolefins including polyethylenes and polypropylenes, polyesters, and polyamides, and, copolymers, mixtures, and blends of such polymeric materials.
In preferred embodiments, structure of at least one of the first and second thin-section elements comprises a fibrous web defining a multiplicity of randomly-spaced small openings extending from a major surface of the web into the interior portion of the web.
In a second family of embodiments, ones of the transfer and dissipation elements extend across the width of the bond pattern, from loci proximate the side edges, at angles of about 10 degrees to about 65 degrees, preferably about 15 degrees to about 50 degrees, more preferably about 20 degrees to about 40 degrees, and optionally about 30 degrees, with respect to the longitudinal axis. A bond width is defined by the width of the pattern perpendicular to the longitudinal axis, including spaces between bond elements, at any point along the length of the pattern. The bond width extends a long the pattern width. Bond element contact lengths are correspondingly defined a long the bond width. The combination of the bond element contact lengths along a respective bond width defines a composite contact length for the respective bond width. The composite contact length, taken at equally spaced intervals along the length of the bond pattern, defines an average composite contact length along the length of the bond pattern. Each composite contact length at a given point along the length of the bond pattern varies from the average composite contact length by no more than about 13 percent, preferably no more than about 10 percent, and more preferably no more than about 8 percent.
In some embodiments of this family, the bond pattern comprises, as first ones of the bond elements, a first sub-array of longitudinally-oriented separate, distinct, and spaced stress receptor elements disposed along the length of the bond pattern, proximate the side edges of the bond pattern and, as second ones of the bond elements, a second sub-array of longitudinally-oriented separate, distinct, and spaced transfer and dissipation elements disposed along the length of the bond pattern, inwardly of the side edges and, correspondingly, generally inwardly of the stress receptor elements. Respective ones of the transfer and dissipation elements have spaced first and second ends, and legs extending from the respective ends toward each other and outwardly of the longitudinal axis along the length of the bond pattern to outwardly-disposed portions of the legs disposed between the stress receptor elements.
In preferred embodiments, the stress receptor elements alternate along the length, and on opposing side edges, of the bond pattern. An imaginary contact line spanning the width of the bond pattern at a given locus along the length of the bond pattern intersects a stress receptor element on a given side of the bond pattern, and also intersects, on the opposing side of the bond pattern, an outwardly-disposed portion of a respective leg of a corresponding transfer and dissipation element. In combination, the distance between distal ends of the most remote ones of the bond elements along a respective imaginary line spanning the width of the bond pattern so defined represents at least about 70 percent, preferably at least about 80 percent, more preferably at least about 85 percent, of the width of the bond pattern. The distance between distal ends of the most remote ones of the bond elements along a respective imaginary line spanning the width of the bond pattern so defined can comprise as much as 90 percent, or 95 percent, and up to 100 percent of the width of the bond pattern. As a result, outwardly-disposed portions of the legs provide balancing support on opposing sides of the longitudinal axis from respective stress receptor elements or legs of respective transfer and dissipation elements, during formation of the bond pattern.
In some embodiments, ones of the transfer and dissipation elements extend from loci proximate the side edges up to loci proximate the longitudinal axis.
In some embodiments, increases and decreases in power distribution across the width of the bond pattern can be defined by variations in composite contact lengths as compared to the average composite contact length for a given bond pattern for at least a complete circumferential rotation of a rotary anvil. Variations in composite contact lengths of the bond pattern reflect no more than about 13% of the average composite contact length of the bond pattern throughout the complete circumferential anvil rotation.
In a third family of embodiments, respective transfer and dissipation elements have spaced first and second ends, and legs extending from the respective first and second ends toward each other and outwardly of the longitudinal axis along the length of the bond pattern to outwardly-disposed portions of the legs, joined to each other, between the stress receptor elements. Such stress transfer and dissipation elements direct stresses inwardly into the interior of the bond pattern.
In preferred embodiments, the first and second ends of the transfer and dissipation elements dissipate the stresses primarily on the interior of the bond pattern.
In other embodiments, ones of the transfer and dissipation elements extend from loci proximate the side edges up to loci proximate the longitudinal axis.
In a fourth family of embodiments, respective transfer and dissipation elements have first ends disposed on the interior of the bond pattern, the respective transfer and dissipation elements extending to second ends adjacent the side edges of the bond pattern between respective ones of the stress receptor elements.
In a fifth family of embodiments, a steady power distribution across the width of the bond pattern defines minimum variations in composite contact lengths as compared to the average composite contact length for the bond pattern for at least a complete circumferential rotation of a rotary anvil reflecting the bond pattern, wherein variations in composite contact lengths of the bond pattern reflect no more than about 13 percent of the average composite contact length of the bond pattern throughout the complete circumferential anvil rotation.